import java.util.Scanner;

public class C_1865 {
	static int num;
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		dfs(sc.nextInt());
		System.out.println(num);
	}
	static void dfs(int n) {
		if(n<0)
			return;
		if(n==0)
			num++;
		dfs(n-2);
		dfs(n-1);
	}

}
